In conventional gas turbine aircraft engines, three primary designs for check valves are used in piping for delivering air to a pressurized cavity: the side hinge clam shell valve, the side hinge flapper valve and the center hinge flapper valve. The primary design criteria for any of these valves include the following: forward flow pressure drop, backflow leakage, cost, maintainability, reliability and weight.
When any one of the aforementioned conventional check valves is installed in piping, any steps or obstructions in the airflow path will contribute to pressure drops in the pipe flow and a less efficient system. Test data indicate that the side hinge flapper valve causes a significant reduction in the pipe flow, the side hinge clam shell valve causes very little drop in the pipe flow and the center hinge flapper valve causes a reduction in pipe flow which is only slightly greater than that caused by the side hinge clam shell valve.
With respect to backflow leakage, the center hinge flapper valve has been shown to be somewhat better than the side hinge clam shell valve. It is also significantly lower in cost than either the side hinge clam shell valve or the side hinge flapper valve. The center hinge flapper valve and the side hinge clam shell valve are similar in maintainability and reliability, whereas the side hinge flapper valve is less reliable in view of apparent field wear problems. The center hinge flapper valve is slightly lower in weight.